1. Field of the Invention
The present invention relates to a deposition-preventing part (e.g., masking tool, shielding ring, shutter, etc.) which is used over an area to be protected from adhesion of a physical vapor deposition film when a physical vapor deposition apparatus is used to form a physical vapor deposition metal film, particularly a physical vapor deposition noble-metal film, as a reflective film on the surface of the substrate of a CD-ROM (read-only compact disc), CD-R (recordable and regenerable compact disc), or CD-E (erasable compact disc) (hereunder collectively referred to as CD), and further to a masking tool for physical vapor deposition apparatuses for noble metals, particularly Au.
2. Description of the Related Art
Preparation of CDs, such as CD-ROMS, CD-Rs and CD-Es, with physical vapor deposition Au films formed as reflective films on the substrate surfaces has been well known, and physical vapor deposition apparatuses for Au which are used for the preparation are, as illustrated in FIG. 1, each composed of a shielding ring 5 for preventing adhesion of a physical vapor deposition Au film on the inner wall of the vessel (not shown) of the physical vapor deposition apparatus for Au, a shutter 6 for temporarily stopping the flow of active Au metal 7 which is generated from the Au target when a CD prepared with a ring-shaped physical vapor deposition Au film 4 formed on the surface of the CD substrate 1 is replaced by a fresh CD substrate 1.
In order to form the ring-shaped, physical vapor deposition Au film 4 on the surface of the CD substrate 1 using an apparatus of the type mentioned above for physical vapor deposition of Au, as illustrated in FIG. 1, the active Au metal 7 which has been generated from the Au target 3 is deposited by physical vapor deposition on the CD substrate 1 which has a masking tool 2 overlaid thereon and is placed in the shielding ring 5 of the physical vapor deposition apparatus for Au.
The masking tool 2 which is overlaid on the CD substrate 1 can be prepared with any metallic material, but is mainly made of Cu or a Cu alloy, and as illustrated in the perspective view in FIG. 2, it comprises a disc-shaped center masking shield 21 and a ring-shaped peripheral masking shield 22, with such a configuration that the center masking shield 21 and the peripheral masking shield 22 are attached concentrically and so as to form a ring-like opening 23 between the center masking shield 21 and the peripheral masking shield 22, and the center masking shield 21 is supported, via a support 26, by a supporting arm 25 which extends from a peripheral barrel 24.
When the masking tool 2 constructed in this way is overlaid on the CD substrate 1 and a ring-shaped physical vapor deposition Au film 4 is formed on the surface of the CD substrate 1, the physical vapor deposition Au film 4 naturally adheres to the surface of the overlying masking tool 2 as well. The physical vapor deposition Au film 4 which has adhered to the surface of the masking tool 2 is of course recovered, and known methods for the recovery include a) recovering by mechanical peeling such as sand blasting; b) formation of an aluminum film on the surface of the masking tool and recovering of the physical vapor deposition Au film formed on the aluminum film through dissolution of the aluminum film in an aqueous NaOH solution; c) use of a masking tool with an electroplating layer of a metal of the platinum group (Pt, Rh, Ir, Ru, etc.) formed on the surface and recovering of the Au which has adhered to the surface of the masking tool by physical vapor deposition, using a commercially available gold-removing agent.
After the Au formed by physical vapor deposition has been recovered and removed according to any of the above-mentioned methods, the masking tool is reused. In summary, known masking tools of the prior art include masking tools consisting only of masking tool substrates made of Cu or a Cu alloy, masking tools comprising aluminum films formed on the surfaces of the masking tool substrates made of Cu or a Cu alloy, and masking tools comprising electroplating layers of a metal of the platinum group (Pt, Rh, Ir, Ru, etc.) formed on the surfaces of the masking tool substrates made of Cu or a Cu alloy.
Recovering by mechanical peeling such as sand blasting, however, is not preferred as a method of recycling expensive masking tools over the long term, since masking tools, which must have high dimensional precision and high levels of surface evenness, have extremely shorter working lives due to deformation or reduction in size after repeated recycling. In addition, recovery of Au from powder resulting from processing by sand blasting can be accomplished only with poor efficiency, since many steps are required for the recovery due to inclusion of Cu or a Cu alloy in the powder deriving from the masking tools.
On the other hand, the method of forming an aluminum film on the surface of the masking tool by physical vapor deposition and forming an Au film on the aluminum film by physical vapor deposition, has a drawback in that a fresh aluminum film must be formed each time the masking tool is used after recovery of the physical vapor deposition Au film, the regenerated masking tool must be stored with care since the formed aluminum film tends to change into an alumina coating, and further the Cu base can undergo corrosion due to immersion in an NaOH solution for recovery.
Accordingly, the most often used method is currently the one described in c) above, where a masking tool with an electroplating layer of a metal of the platinum group formed thereon is used, and the masking tool with Au adhering thereto by physical vapor deposition is immersed in an aqueous solution of a commercially available gold-removing agent, KCN and NaOH which is kept at 50.degree. C. or lower, and the Au which has adhered by physical vapor deposition is recovered as a cyanogen complex. However, since electroplating layers of metals of the platinum group have remarkably different plating-layer thicknesses depending on the configurations of the substrates, it has been difficult to obtain uniform electroplating layers of metals of the platinum groups.
For example, one problem has been that when masking tool substrates made of Cu or Cu alloys have pinholes or acute portions in the surfaces, the electroplating layers of metals of the platinum group on such portions become extremely thin, and dissolution and corrosion of the masking tool substrates made of Cu or Cu alloys start at these thin portions of the plating layers, thus reducing the number of times the masking tools can be recycled.